1. Technical Field To Which The Invention Belongs
The present invention relates to a magneto-optic recording medium and an optical information recording/reproducing apparatus for high density optical recording and reproducing to which the land- and/or groove-recording in a magneto-optic recording medium is applied.
2. Prior Art
At present, optical recording media are popularly used as recording media from which audio and video signals can be reproduced. In particular, magneto-optic recording media and phase change recording media are studied and developed in various places as rewritable, high-density recording media.
In order to enhance the recording intensity of an optical recording density of an optical recording medium in which information is recorded spirally or concentrically, there are considered to be two methods, i.e., the shortening of the track pitch and the enhancement of the linear recording density. In either case, the recording density of the optical recording medium can be realized by shortening the wavelength of the semiconductor laser used for recording and reproduction, but it seems to take some more time before semiconductor lasers with short wavelengths of green or blue color which can continuously oscillate at room temperature over a long time and, further, come to be sold at low prices at the market. Under such circumstances, methods are grouped according to which the recording density can be substantially improved by the use of lasers operating with presently used wavelengths, as in the case of MSR (magnetic super-resolution), in magneto-optic recording media.
In case of a RAM medium, such as a magneto-optic recording medium, light of the same wavelength is used both for the writing of information and for the reading thereof, whereas in case of a ROM medium in which information is recorded in advance, phase pits are formed by the use of a short-wavelength gas laser, i.e., Ar. In view of the ROM medium, it is true that, in case the ROM medium, the reproducing condition is the same, but recording is made therein, as it were, using, as it were, a light source which will become usable in the future; in respect of recording information at a high density, the RAM medium is disadvantageous. Due to this, in the standards for DVD which attract attention as next-generation video recording media for domestic use, no proposal has been made at present on a structure in which the recording capacity of DVD-ROM medium can be supported by a RAM medium of the same medium size.
The land and groove record can be simply doubled in its record density if the linear recording density is the same and the track pitch is the same, and therefore, the land and groove recording is a very important method in view of the development of a high-density recording medium. In this connection, it is reported that, in a magneto-optic recording medium, the MSR mentioned above can not only reduce the linear recording density, but also enhance the inter-track crosstalk, and thus the applicability thereof to the land and groove recording is examined at various places. However, the conditions for allowing a magnetic super-resolution to manifest itself-such as, e.g., the case where the reproducing laser power depends on the linear velocity, the case where a reproducing magnetic field is necessary, the case where at least three magnetic layers are necessary, etc.--are very complicated, there is an uncertainty in respect of stability, and the manufacturing costs tend to become high.